Scilab Function
Last update : April 1993

eqiir - Design of iir filters

### Calling Sequence

  `[cells,fact,zzeros,zpoles]=eqiir(ftype,approx,om,deltap,deltas)`

### Parameters

- `ftype`: filter type (`'lp','hp','sb','bp'`)
- `approx`: design approximation (`'butt','cheb1','cheb2','ellip'`)
- `om`: 4-vector of cutoff frequencies (in radians) `om=[om1,om2,om3,om4]`, `0 <= om1 <= om2 <= om3 <= om4 <= pi`. When `ftype`='lp' or 'hp', `om3` and `om4` are not used and may be set to 0.
- `deltap`: ripple in the passband. `0<= deltap <=1`
- `deltas`: ripple in the stopband. `0<= deltas <=1`
- `cells`: realization of the filter as second order cells
- `fact`: normalization constant
- `zzeros`: zeros in the z-domain
- `zpoles`: poles in the z-domain

### Description

Design of iir filter interface with eqiir (syredi)

The filter obtained is `h(z)=fact`*product of the elements of `cells`.

That is `hz=fact*prod(cells(2))./prod(cells(3))`

### Examples

    [cells,fact,zzeros,zpoles]=...
    eqiir('lp','ellip',[2*%pi/10,4*%pi/10],0.02,0.001)
    transfer=fact*poly(zzeros,'z')/poly(zpoles,'z')

### See Also

`eqfir`, `iir`,